The present invention can be used for recording and reproducing systems such as VTRs for broadcasting service and business use and is particularly effective to carry out good time base correction.
VTRs used for the broadcasting service today employ tapes of 1" and 2" widths, which are the mainstream, while the video signal recording systems employ the system which directly modulates the frequency of the composite video signal.
During such recording and reproducing processes, a time base variation is caused by uneven head rotation, uneven tape running and the like. Such a variation is corrected during reproduction by the time base corrector (TBC) by means of the horizontal synchronous signal or burst signal in the reproduced video signal. With this system, however, the color signal in the case of the NTSC system is modulated using the quadrature phase by a 3.58 MHz subcarrier and added to the luminance signal. For this reason, the color signal, when frequency modulated, is far from the FM carrier, thereby causing insufficient reduction of the noise which is the feature of FM, while the color subcarrier varies the phase by as much as the residual jitter of the TBC and this phase variation generates the phase noise causing insufficient convergence of the color vector.
In view of these points noted above and to improve the amplitude of the color signal and S/N in the phase direction and to further enhance the convergence of the color vector, a system is available as a recording system wherein even the two components of the color signal are recorded using frequency modulation, time base corrected during reproduction, modulated (encoded) by the reference subcarrier and added to the luminance signal to thereby produce the composite video signal. By this system, because the color signal (in this case, the color signal is one of the component signals) is recorded using frequency modulation by the base band, the color signal is reproduced with a good S/N. Furthermore, because the color signal is encoded by the reference subcarrier, the phase signal is not generated and a color signal of good reproduction can be obtained.
An example of this system is shown in FIG. 1 for explanation.
In FIG. 1, the terminals 1, 2, and the 3 are luminance signal (Y), R-Y signal, and the input terminal of the B-Y signal respectively; element 25 is a synchronizing signal generator; element 5 is a time base compressor; element 4 and 6 are frequency modulators; elements 7 and 8 are heads; elements 9 and 10 are frequency demodulators; elements 11 and 12 are TBCs; elements 14 is a reference signal input terminal; elements 15 is a synchronizing generator; element 16 is an encoder; and elements 1, 19, 20 and 21 are Y, R-Y, B-Y signals and an output terminal of the composite image signal. The Y signal applied to the terminal 1 is modulated by the frequency modulator 4 and recorded on the tape by the head 7. On the other hand, the R-Y signal (See FIG. 2(a)) and B-Y signal (See FIG. 2(b)) which are the components of the two color signals applied to the terminals 2 and 3, and the R-Y signal is added by means of the adder 26 to the synchronizing signal generated by the synchronizing signal generator 25 from the horizontal synchronizing signal, time base compressed to 1/2 of 1 line by the time base compressor 5, turned into one signal (R-Y represents the R-Y signal compressed into 1/2 line) in such orders R-Y.B-Y.R-Y.B-Y . . . (See FIG. 2(c)), modulated by the frequency modulator 6, and recorded on the tape by the head 8.
The luminance signal and color signal form separate tracks by means of the head 7 and head 8, and are recorded on the tape. During the reproduction, the Y signal reproduced by the head 7 is demodulated by the frequency demodulator 9 and time base corrected by the TBC 11. The color signal reproduced by the head 8 is demodulated by the frequency demodulator 10, time base corrected by the TBC 12, and expanded to the original time base. The TBCs 11 and 12 write signals into the memory by the write clock generated from the horizontal synchronizing signal in the reproduced and demodulated signal and read out the signal from the memory through the read clocks 22 and 23 generated by the synchronizing generator 15 from the reference signal applied to the terminal 14, thereby performing the time base correction and expanding operation. At this stage, the synchronizing signal is rejected and the reference synchronizing signal 24 generated from the synchronizing generator 15 is added to the Y signal by the adder 13. In this manner, signals are replaced with the synchronizing signal without noise so that the reproduced signals Y, R-Y and B-Y are obtained on the terminals 18, 19 and 20. On the other hand, the signals R-Y and B-Y, the output of the TBC 12, are encoded by the encoder 16 through the reference subcarrier 27 generated by the synchronizing generator 15, added with the Y signal by the adder 17, and the reproduced composite video signal is obtained on the terminal 21.
By this system, however, because the TBC generates the write clock only by the horizontal synchronizing signal in the reproduced signal, it is difficult to follow the jitter of the signal completely. Because the synchronizing signal is added anew by the adder 26 when the R-Y signal of the output of the terminal 19 is applied to be recorded next on the VTR during dubbing, the coupled errors during the dubbing, if repeated, accumulate causing the time base correction characteristic to be degraded during the dubbing, which is a problem.